The proposed research shall characterize a new model system for the cytogenetic analysis of the origin of aneuploidy which arises during the first meiotic division in mammalian oocytes. This new system is based upon the recent observation that porcine oocytes exhibit a very high incidence of nondisjunction at the first meiotic division when isolated from ovarian follicles and matured in the presence of 1-glutamine in vitro with a highly defined procedure of cell culture. Oocytes matured in control culture medium exhibit very high incidences of apparently normal ploidy at the conclusion of first meiotic division. This new system offers a unique approach to the analysis of nondisjunction in the mammalian oocyte; and it employs a natural compound, an amino acid, as compared with other systems which employ mitotic poisons. It is proposed first that this new model be defined concerning optimal amino acid concentration, timing of exposure, specificity of effector molecule, species variation among several mammals and reversibility. Secondly the ultrastructural correlates of nondisjunction and normal first meiotic division arising predictably in this system shall be investigated. Thirdly the proposed research shall examine the mechanisms by which an amino acid interacts with the mammalian oocyte, and the means by which the amino acid or its metabolite induces nondisjunction. The proposed research promises to produce a characterized model system which in the future can be exploited in the evaluation of potentially harmful agents of wide variety on mammalian gametes.